Magnetic ion traps, or Penning traps, serve to confine ions for long periods of time, to cause them to react with neutral gases, so that they can subsequently be selected by their mass and thus detected with very high resolution in terms of mass.
They are used in a variety of fields going from atomic physics to proteomics.
The advantage of such devices for characterizing macromolecules leads to using magnetic fields of ever increasing intensity so as to increase sensitivity, resolving power and the range of masses that can be detected. High intensity fields, at present of the order of 12 Tesla, are obtained using superconductor magnets. Such devices are bulky and can weigh as much as several (metric) tonnes. In addition, they require complex power supply and cooling installations, and they are therefore usable only in fixed installations.
Traps of smaller size, suitable for providing a mobile device, have been developed by using permanent magnets to generate the magnetic field (L. C. Zeller, J. M. Kennady, J. E. Campana, H. I. Kenttamaa, Anal. Chem. 1993, 65, 2116-2118, U.S. Pat. No. 5,451,781 DIETRICH).
Nevertheless, when the magnetic field is restricted to values of about 0.4 Tesla and/or to values that are too small, performance is very limited.
In order to obtain good performance, in particular concerning resolution, a fundamental parameter is good uniformity of the magnetic field, and a field intensity of about 1 Tesla is often considered as being a necessary order of magnitude.
The permanent magnet described in French patent application FR 2 835 964 serves to obtain a uniform field of good quality and intensity, but the geometry used limits use of the trap to ions that are formed directly in the cell or in its immediate vicinity.